What is the cdc, and what does it have to do with healthy weight levels?

The CDC is the government organisation in charge of public health. For example if a contagious virus such as Ebola were to break out in America, they would be the ones working on a vaccine and a cure.

They also set the BMI scale I believe, which is an equation that tells you your weight conpared to your height and shows it in several ranges from underweight to morbidly obese.

If it's a smaller child or infant, place one on the middle of the chest and on the child's back. (if it is a bigger child with enough room for two, place one on the upper right/your left of the chest, and one on the lower left/your right) the pads should never touch each other.